The present invention relates to a semiconductor device promoting dense and highly integrated packaging and a method of producing the same and, more particularly, to the structure of contact portions of a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) with trench isolation and a method of producing the same.
A semiconductor device with an isolation region formed by trenches is conventional. The trenches are formed in the surface of a semiconductor substrate and then filled with silicon oxide. After a gate electrode and diffusion layers have been formed, the entire surface of the resulting laminate is covered with an interlayer insulation film. Contact holes are formed in the insulation film. A metal film is formed in the contact holes and then patterned to form wirings. The problem with this semiconductor device is that a junction leak current characteristic deteriorates due to the progress of microstructure which is derived from the high integration of semiconductor devices. Specifically, because the dimensions of the semiconductor device, as seen in a plan view, are reduced due to the progress of microconfiguration, a margin for the positional deviation between the contact holes and the diffusion layers is reduced. As a result, the contact holes are apt to partly extend to the outside of the diffusion layers. It follows that a metal film for wiring filled in the contact holes short-circuits the substrate and diffusion layers, aggravating the junction leak current problem.
Japanese Patent Laid-Open Publication No. 62-190847 proposes a solution to the above problem. Specifically, in this document, a silicon nitride film intervenes between a silicon oxide film filling an isolation region and a substrate. This kind of scheme, however, brings about another problem that a difference between the coefficient of thermal expansion of the substrate and that of the silicon nitride film is noticeable and introduces defects in the substrate during heating due to a thermal stress. The defects also aggravates the junction leak.